1. Field of the Invention
The present invention relates to a rotary encoder.
2. Description of the Related Art
Rotary encoders are commonly used in a variety of applications. For example, many electronically-controlled cameras use a rotary encoder. An electronically-controlled camera uses electronics circuitry for controlling operations of the camera. When the user of the camera wishes to take a picture at his desired aperture or shutter speed, and/or with a certain correction to the exposure value, he/she has to enter corresponding parameter(s) into the electronics circuitry. The entry of parameters is often made using a dial supported on a rotary shaft, which is typically connected to a rotary encoder for converting angular positions of the dial into corresponding electrical signals.
A rotary encoder for use in a small-size electronic apparatus, such as an electronically-controlled camera as described above, is required to be compact among others requirements.
A typical rotary encoder for such purposes comprises a rotary shaft adapted to be supported for rotation about its axis, a disk fixedly secured to the rotary shaft and made of an insulating substrate with a conductive pattern formed on a side surface thereof, and a plurality of electrical contacts adapted for fixed mounting and so arranged as to be in contact with the conductive pattern depending on the angular position of the disk such that various combinations of the electrical contacts may be electrically interconnected one another depending on the angular position of the disk.
For a small-size rotary encoder having this arrangement, the reduction in volume of the structure for securing the disk to the rotary shaft is critical because the relative volume of this structure to the overall volume of the rotary encoder increases as the latter volume is decreased.
One typical structure for securing the disk to the rotary shaft includes mating portions formed on the disk and the rotary shaft and a single set screw for retaining the disk to the rotary shaft. The mating portions serve to define the relative angular position of the disk to the rotary shaft and prevent any angular displacement between them. The disk has a central hole formed therein and the rotary shaft has an axially-extending, central threaded hole formed therein. The set screw is passed through the hole in the disk and threadably engaged into the threaded hole in the rotary shaft.
However, since such a single set screw engaged into a central threaded hole in the rotary shaft is subject to unintentional loosening during use, a relatively large set screw is required for this purpose, resulting in a large volume of the structure for securing the disk to the rotary shaft and thus in a large overall size of the rotary encoder.
Use of two or more set screws located off-center with respect to the rotational center of the disk may be effective for preventing unintentional loosening and smaller set screws may be used in such arrangement. However, this arrangement may raise another problem that any set screws so located goes around the rotational center of the disk, which requires more space on the disk, still resulting in a large overall size of the rotary encoder.